Cohort trials have shown evidence that obesity and a low level of physical activity are not only associated with a higher risk of developing breast cancer, but also with an increased risk for recurrence and reduced survival in breast cancer patients. The SUCCESS C study is the first European trial to evaluate the effect of an intensive lifestyle intervention program on disease-free survival in women with early breast cancer and to examine the predictive value of selected biomarker candidates. A total of 3,547 women with early-stage, Her2/neu-negative breast cancer will be included. The first randomization will compare disease-free survival in patients treated with either 3 cycles of FEC (epirubicine, fluorouracil, cyclophosphamide), followed by 3 cycles of docetaxel or 6 cycles of docetaxel-cyclophosphamide, and thus assess the role of anthracycline-free chemotherapy. The second randomization compares disease-free survival in patients with a body mass index of 24-40 kg/m(2) receiving either a telephone-based individualized lifestyle intervention program aiming at moderate weight loss or general recommendations for a healthy lifestyle alone. In addition, the study will evaluate the predictive role of cancer-associated and obesity-related biomarkers for the prediction of disease recurrence and survival. This SUCCESS C trial will provide valuable information on the effects of a lifestyle intervention program on the prognosis of early breast cancer patients.